by Kim Hjelmgaard, USA TODAY

by Kim Hjelmgaard, USA TODAY

President Obama arrived in Estonia Wednesday where he will hold security talks with the leaders of the three Baltic countries that sit on Russia's western frontier.

Estonia, Latvia and Lithuania have been pressing NATO to establish permanent military bases in the region to counter Russian aggression in Ukraine, and to prevent further incursions by Moscow across previously Kremlin-controlled territory.

Several hours after Obama landed in Estonia, Ukrainian President Petro Poroshenko said he reached a permanent cease-fire agreement with Russian President Vladimir Putin over the conflict in eastern Ukraine. However, the Kremlin subsequently denied that a truce had been reached, saying only that peace talks had been discussed.

Speaking alongside Estonian President Toomas Hendrik Ilves in a news conference in Tallinn Wednesday, Obama announced plans to send more Air Force units and aircraft to the Baltics. He said Estonia's Amari Air Base was an ideal location to base those additional forces.

"It is unbreakable, it is unwavering, it is eternal. And Estonia will never stand alone," Obama said of the U.S.'s NATO pledge to defend its allies.

Around a third of Estonia's 1.3. million residents are Russian-speaking and all three Baltic states have historic ties to Russia. Much to the annoyance of Russia, Estonia, Latvia and Lithuania are members of NATO as well as the European Union. Ukraine is not a member of NATO or the EU.

The legality of the U.S.'s duty to defend the Baltics in the event of Russian attack would be underpinned by NATO's Article 5, which states that an attack on one member is considered an attack on the entire alliance.

Under a separate NATO charter, the alliance created in the wake of World War II to contain militarism across Europe is not permitted to establish permanent military bases in eastern and central Europe.

The president's trip to Estonia comes as the 28-nation military alliance is preparing for a summit in Wales on Thursday and Friday that has been described by NATO's former top military commander Adm. James Stavridis as "the most important since the fall of the Berlin Wall."

The crisis in Ukraine and attempts to curb what Stavridis called "Russian adventurism" will be a major point of discussion in Wales but so will the growing threat of the Islamic State in Iraq and Syria. On Tuesday, the IS claimed in a video to have beheaded a second American journalist.

The White House said Wednesday that the video was authentic and Obama said in Estonia that the U.S. will work to build a coalition that will "degrade and destroy" the militant group responsible.